In the past number of years there has been a continuaously increasing surge of interest in winter sports activities, particularly those activities which need a snow base for operation, e.g., skiing, snowmobiling, snowshoeing and the like. Unfortunately, in many areas of the world the natural snow fall is not predictable nor sufficient to assure continuous operation during the season of sports areas and resorts having facilities for such winter sports.
In more recent years continuity of operation and a good snow base have been gained by the use of artificial snow-making machines and apparatus. With such equipment snow-based winter sports activities have been continuously operated during the winter season and extended to geographical areas of the United States as far south, for example, as North Carolina, Virginia and Tennessee even though there is usually not sufficient natural snow in these areas to permit such sports on a regular basis during the season.
With artificial snow making equipment it is essential only that there be an ambient temperature below about 32.degree. F. (0.degree. C.) for a period sufficient to permit snow making to continue until an adequate depth of snow is deposited on the area, terrain or slope desired to be covered. In areas of North Carolina and Tennessee, for example, during a typical winter sports season there may be only 25 days with good conditions for making artificial snow. Farther north in Ohio 30 to 40 days for snow making operations ordinarily can be expected and in Michigan 50 days or more are not uncommon. Therefore, it is important for effective operation that large volumes of snow be made rapidly during those periods when conditions are right for mechanical snow making.
The snow making methods, apparatus and machines which have gained widespread commercial acceptance fall into two types, those which use compressed air in greater or lesser amounts and those which use no compressed air. This invention relates to those snowmaking methods, apparatus and machines that utilize compressed air.
Illustrative of one category of such methods and apparatus utilizing compressed air in a so-called "snow making gun" is that disclosed by Pierce in U.S. Pat. No. 2,676,471. This machine mixes compressed air with water within a spray nozzle to effect particle formation of the water along with a cooling of the water which results from the adiabatic expansion of the compressed air. In commercial practice it has been found that the Pierce machine and its successors are highly susceptible to nozzle freezing. The aforementioned Pierce U.S. Pat. No. 2,676,471 illustrates an early, if not the earliest, embodiments of a typical compressed air snowmaking gun. A more recent version of such a snow gun is that disclosed in Ratnik U.S. Pat. No. 3,829,013.
Another category of methods and apparatus for making and disposing snow uses compressed air but in much smaller quantities due to provision of a large fan or blower as described in Hanson U.S. Pat. No. 2,968,164, Jakob et al U.S. Pat. No. 3,596,476, Eustis et al U.S. Pat. No. 3,703,991, Rice U.S. Pat. No. 3,838,815 and Kircher U.S. Pat. No. 3,979,061. The most recent and improved form of such fan-type snow machines is that covered in the Kircher et al U.S. Pat. No. 4,105,161 which discloses, inter alia, a fan, an air-water seeder gun and bulk water manifold. While this Kircher et al method and machine is very energy efficient and capable of improved performance even under adverse temperature and humidity conditions, the relatively low water flow going through the "miniature" air-water snow gun utilized as a seeder in said apparatus has been found to cause seeder freeze-up problems in some applications.
One prior art attempt to prevent freeze-up in a fan-type snowmaking machine is that disclosed in the Rambach U.S. Pat. No. 3,945,567, which is assigned to the assignee hereof. In the Rambach patent pressurized water is circulated in a first manifold past a plurality of bulk water spray nozzles which extend in part through the water manifold and then the bulk water is fed to a second manifold with which the bulk water spray nozzles communicate. The water circulating in the first manifold maintains the temperature of such nozzles at a level above freezing so as to prevent clogging thereof by formation of ice therein. The snow machine of the Rambach patent also has a seeder snow gun 21 disposed interiorly of the fan cowling 20, and water is delivered to the mixing chamber of the seeder by a tap off connection to the main water manifold so as to circulate through a chamber 35 disposed forwardly and spaced from the mixing chamber 41 and exit orifice 43 of the seeder gun. Chamber 35 surrounding the forward end of the seeder forms a water jacket around the barrel to maintain the discharge orifice 30 thereon at a sufficiently high level to prevent any ice formation thereof.
However, in accordance with the present invention, it has been found that the main freeze up or clogging problem in compressed air-water snow guns, whether of the bulk snowmaking type or miniature seeding type, occurs primarily in the mixing chamber itself as well as close to the exit orifice leading directly from the mixing chamber, and in some cases in the air and water lines in the portions thereof in close proximity to the mixing chamber.
The purpose of this invention is to avoid such freeze-up problems in compressed air-water snow making guns whether used alone or as seeders in fan-type snow machines. Such freeze-up problems are avoided by employing apparatus and a method of making snow wherein compressed air and pressurized water are first mixed in some form of nozzle constituting a snow gun or seeder and the resulting mixture expelled into ambient air having a temperature below 32.degree. F. The present invention thus involves an environment of a pressurized water source, a compressed air source, a mixing chamber and an exit orifice, and embodies the improvement of providing a continuous flow of water substantially surrounding said mixing chamber and at least a portion of said exit orifice in an amount and at a temperature sufficient to prevent clogging due to freezing of said water and said mixture prior to discharge thereof from said exit orifice.
It is believed that the basic theory of the present invention is, in a sense, exemplified by Lake Michigan. Even in the coldest of winters Lake Michigan does not freeze solid because of the large mass of water involved. The present invention flows or maintains a relatively large mass of water around those portions of the air-water gun more likely to freeze. This large mass of water has been designated herein as the reservoir and acts as an anti-freeze-up heat source in somewhat the same manner as Lake Michigan does, and thus eliminates the need for any auxiliary source of heat or anti-freeze chemicals such as have been employed in the past to overcome this problem.
Accordingly, the aforementioned terminology "surrounding at least a portion of the exit orifice" is intended to mean that the typical nozzle which is used in air-water snow guns has, when embodying the present invention, at least the base thereof surrounded by said reservoir. Moreover, although there are many exit orifice designs known in the patent literature as well as in commercial usages, it is a feature of this invention that the reservoir extend to within at least one inch (25.4 mm) of that area where the air-water mixture is expelled to ambient air at ambient pressure. Any snow making gun at rest has an exit orifice which is exposed to ambient air and located at least functionally between the mixing chamber and the outside air. In most practical applications of the invention it has been found that this point in space defines the one inch limit for the reservoir to surround a portion of the exit orifice. In other words, it is contemplated that, consistent with practical design and engineering constraints, enough of the reservoir structure surround the exit orifice as well as mixing chamber to preclude freeze-up of the nozzle or gun, such freeze-up being prevented or precluded by a heat transfer relationship from the reservoir to the structure of the mixing chamber and exit orifice.
Another feature of the present invention resides in the circulation of the water through the reservoir on its way to additional snowmaking bulk water nozzles, such that the flow rate of water through the reservoir is at least twice that of the flow rate of water into the mixing chamber of the snow gun per se, and preferably the flow rate of water circulating through the reservoir is many times that of the flow rate of the water into the mixing chamber, such as in the order of 7 to 1 up to 20 to 1 and even higher.
In accordance with another feature of the invention when applied to a snow gun of the aforementioned Pierce/Ratnik type used for making bulk snow, rather than for seeding in conjunction with a fan-type machine, all of the bulk water being fed to the snow gun is first circulated through the reservoir and then admitted to the mixing chamber of the snow gun.
In accordance with a further feature of the invention, the compressed air source is connected to the mixing chamber by a conduit which contains a back check valve which in turn is also disposed in the reservoir to prevent freeze-up. In addition, the pressurized water source is coupled to the mixing chamber via a conduit containing a pressure regulating valve which also is disposed within the reservoir to prevent freeze-up of the valve.